Your RAM MEMORY is not listed under ASRock Motherboard QVL List for Pinnacle Processors: ASRock > B450 Pro4
These are the only 16 GB RAM MEMORY with HX426C part numbers.
Try installing just one 16 GB RAM MEMORY and see if it works correctly. IF it does then that probably indicates that the motherboard isn't compatible with 2 x 16gb RAM MEMORY of the Specific RAM part number that you are using.
The QVL List are RAM MEMORY that has been TESTED by ASRock to be compatible with your motherboard.
It is possible this list is out-dated or your RAM wasn't listed because it hasn't been tested yet or it was found to be incompatible.
NOTE: Your latest Motherboard BIOS version for Pinnacle Processors is version 3.50. Any BIOS version above 3.60 ASRock warns about not updating to this version if you are using a Pinnacle Processor:
I would updated the BIOS to version 3.50 and install the latest CHIPSET from ASROCK.
or you could download a newer B450 AMD CHIPSET (03/19/2020) from AMD Download page from here: https://www.amd.com/en/support/chipsets/amd-socket-am4/b450